The present invention relates to power transfer systems for four-wheel drive automotive vehicles and more particularly to a transfer system which enables single control rod shifting of gears between two-wheel and four-wheel high speed drive modes while the vehicle is moving as well as shifting to a four-wheel low speed drive from a stop in addition to providing for release of stressed relationships in the gear system resulting from differentials in movement which may occur between the front and rear output shafts.
It is well established that four-wheel drive vehicles, although highly desirable for off-road travel over rough terrain, because of their greater reliability in traction under such conditions, are much more economically operable on hard, improved surfaces as a two-wheel conventional drive vehicle. Thus capability to shift from four to two-wheel driving and return is desirable.
Prior art gear transfer arrangements enable conversion of such vehicles to two-wheel or four-wheel drive, but have the disadvantage that the position of the locking drive hubs of the usual non-driven wheels must be manually locked or unlocked to correspond to the four or two-wheel drive shift control position selected. Thus conversion from two-wheel to four-wheel and return has been cumbersome, time-consuming and subject to error in combinations of settings required to obtain the wheel-driving relationships desired.
In addition, while operating the vehicle in a four-wheel driving mode, windup stresses are frequently experienced in the gear shifting systems, such as occur during turning of the vehicle. Windup stresses can result from the front wheels travelling over a different distance than the rear wheels during a turn, thereby causing a differential in rotation between the front and rear drive shafts of the gear transfer system. Shifting of gears from four to two-wheel drive under such conditions can be difficult if not impossible until the stresses have been relieved.
In view of the foregoing it is an object of the present invention to provide a transfer gear unit for shifting the driving mechanism of an automotive vehicle to either a two or four-wheel high speed drive mode from the other mode while the vehicle is in motion.
Still another object of the invention is to provide a transfer gear unit for shifting the driving mechanism to either a two or four-wheel drive mode with a single shift control rod without the need for setting external locking hubs on wheels of the vehicle when an internal locking axle, activated by the transfer gear unit is employed.